The depth of the moulds were about twice the thickness of a regular flat axe. We thought that it might provide a reducing atmosphere, so that the upper surface would not oxidise as much. When we tried it out, it worked well and the upper surface was much smoother than if the bronze had been poured right to the surface. However, we did have a constant problem with air bubbles forming on the lower surface (a photo of an example is in O'Kelly and Shell 1978 in "The Origins of Metallurgy in Atlantic Europe" p. 139).
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